The present invention relates generally to the field of data networking. More specifically, the present invention relates to the detection of collisions between transmitted signals on a network.
Ethernet networks implement a Carrier Sense, Multiple Access/Collision Detect (CSMA/CD) protocol to ensure that only one node (or station) of the relevant Ethernet network is propagating a signal over a carrier medium of the network at any given time. As implied by the xe2x80x9cCarrier Sensexe2x80x9d aspect of this protocol, prior to or during signal transmission, a station checks or listens on the relevant carrier medium to determine whether another station is transmitting. Merely for example, an inquiring station may sense a voltage on a network line, and then assume that another station is transmitting.
In view of the distances between stations on a network and finite signal propagation times, it often occurs that a station wishing to transmit will sample the relevant carrier medium, and sense no traffic thereon, even though another station may have begun transmitting. Accordingly, two stations will simultaneously transmit, resulting in a collision of transmitted signals. The delay in detection of transmission of a signal over the carrier medium because of the distance between stations coupled thereto has resulted in a so-called xe2x80x9cslot timexe2x80x9d being defined as a function of the time required for the transmission of a signal by a first station, the possible xe2x80x9cCarrier Sensexe2x80x9d detection of this signal by a second station of the network, and the return of a collision detect signal by the second station to the first station. It will be appreciated that the possibility of colliding transmission signals occurs during this slot time.
In Ethernet networks where the carrier medium comprises a regular and well-designed wiring system, constructed using a high-quality cable, the detection of collisions may be performed by detecting voltage swings on the carrier medium that exceed the voltage that can be generated by one transmitter alone. However, where the carrier medium of the network displays a number of undefined characteristics, the above collision detection methodologies may be unreliable. For example, where the carrier medium comprises existing telephone wiring within a residence (e.g., Plain Old Telephone Service (POTS) wiring), the wiring may comprise unshielded, twisted-pair (UTP) telephone cable and may be either Category One or Category Two cable as defined by the EIA/TIA 568 specification. Accordingly, the wiring may be susceptible to noise. Further, the use of residential telephone wiring as the carrier medium for the network poses a number of problems as the transmission of data signals must occur over an arbitrary, unterminated wiring system with unknown electrical characteristics. This results in impedance mismatches, and the lack of termination contributes significantly to the persistence of reflections of signals and to unpredictable peaks and valleys in frequency response within a band of interest. The power-splitting effect of star configurations, which are commonly implemented in residential wiring, increases these problems.
According to a first aspect of the invention, there is provided a method of detecting a collision between transmissions on a carrier medium within a network. The method commences with the transmission of an identifier from the transmitter of a network device. This transmitted identifier has a predetermined duration, and includes a pulse comprising a multi-cycle waveform and having a temporal location which is specific to the transmitted identifier. A further identifier is received at a receiver of the network device. The received identifier similarly has a predetermined duration and includes a pulse at a temporal location. A determination is then made as to whether the temporal location of the pulse within the received identifier corresponds to the temporal location of the pulse within the transmitted identifier. If the temporal locations of these pulses do not correspond, a collision is detected on the network.
According to a second aspect of the invention, there is provided apparatus for detecting a collision between transmissions on the carrier medium of the network. The apparatus comprises a transmitter, which is coupled to transmit a first identifier over the carrier medium, and a receiver, which is coupled to receive a second identifier. The first identifier includes a pulse comprising a multi-cycle waveform. The apparatus also includes a logic circuit, which is coupled to the receiver, that determines whether the temporal location of the pulse within the second identifier corresponds to the temporal location of the pulse within the first identifier. If not, the logic circuit then detects a collision on the network.
The invention extends to a network adapter, a Network Interface Card (NIC) and a transceiver incorporating the above apparatus.
Other features of the present invention will be apparent from the accompanying drawings and from the detailed description which follows.